Current semiconductor interconnection technology involves mounting integrated circuit (IC) chips on chip carriers like ceramic substrates or assembling the chips into plastic packages. Additionally, interconnection technology often involves mounting the chip and carrier combination on a circuit card. These interconnected components are then used in a variety of electronic applications such as computers, hand held electronic devices and the like. In these applications the useful life of a product often depends on the integrity of the connects interconnecting the components. For the interconnects not only may provide mechanical means for bonding the components together but they also provide the vital electrical paths between the components.
There are three principal systems for connecting IC chips to carriers and a chip and carrier combination to a circuit card. Each system provides both mechanical bonding and electrical connections between the connected structures.
One system is termed a flip-chip bonding system, where metal bumps on the face of the IC chip are connected to metal pads formed on a chip carrier. Interconnection here is typically made by solder bumps (a lead and tin mixture), that comprise a so-called "controlled collapse chip connect" or "C4".
Another system comprises use of solid metal balls, typically to connect a carrier/substrate to a circuit card. In the solid metal ball system, the balls can be composed of copper, gold, aluminum, or solder (such as a 3% tin 97% lead mixture). For assembly, a mask is placed over the substrate or wherever one wants to attach the balls. By readily known processes in the art, the mask either has or is made to have, recesses corresponding to electrical contacts on the substrate. Next, dots of solder are located on the electrical contacts, or alternatively formed before the mask step. The mask surface is then flooded with metal balls, each recess filling with a single metal ball, the excess balls rolling away. Then the balls and the substrate are heated through an ordinary reflow operation causing the balls to bond to the solder dots on the electrical contact. If desired, the mask can be removed. The substrate is then position together with a circuit card so corresponding electrical contacts with solder dots can be connected. The substrate and card are then compressed together and heated to again reflow the metal balls and interconnect the two via the metal balls interconnecting their electrical contacts.
More recently, a third aspect to the existing interconnection systems has come about for interconnecting substrates, namely, conductive adhesives and conductive adhesive balls. For example, adhesive balls eliminate the need for reflowing that traditional metal balls require to interconnect the substrates. The adhesive itself serves to mechanically bond the substrates and electrical connection is made from the substrate electrical contact through the adhesive ball to the electrical contact of the other substrate. Further, in the metal ball system, now dots of conductive adhesive can be used in place of the solder dots. In this way, heating and reflow is not necessary to interconnect the opposing structures. Rather, once the metal balls fill the mask, the two substrates can be pressed together and the adhesive between the electrical contacts and opposite sides of the balls allowed to cure, thereby mechanically bonding and electrically connecting the opposed structures.
There are several problems inherent with the existing interconnection methods and apparatus, and in particular, there is one common problem seen throughout. This problem resides in the basic principle that different structures or substrates, e.g., the IC chip, the carrier and the interconnect itself, often have different thermal expansion characteristics when exposed to the same temperatures. Thus, over time with exposure to everyday operational temperature changes, fatigue tends to corrupt the integrity of the interconnect joining the two structures, causing electrical failure between the structures.
One solution to such a problem would be to maintain the interconnected structures in a stress-free environment during their useful lifetime. Ideally, this means that any and all possible stress factors that could affect the structures or their interconnects must be eliminated. In practice, this is virtually impossible and where possible, only at great expense. Consequently, a more reasonable solution to this problem is needed.
These and other types of interconnection systems and components disclosed in the prior art do not offer the flexibility and inventive features of our invention. As will be described in greater detail hereinafter, the apparatus and methods of the present invention differ from those previously proposed.